The drilling of earth, as in drilling for oil, typically employs a rotary drilling apparatus including a drill bit at its lower end. The rotary drilling apparatus creates a significant amount of heat due to friction during the drilling process. Therefore, a lubricant or "drilling mud" is employed to reduce heat buildup in the drilling apparatus. Also, since the earth formations encountered during drilling can vary widely, drilling muds are selected so as to condition the earth for effective removal of drill cuttings.
An exemplary drilling mud comprises a gelling agent, such as a solid phase bentonite, a weight agent, such as barite, and water. Numerous different additives to this drilling mud are also employed to control viscosity, yield point, gel strength (thixotropic properties), pH, fluid loss, tolerance to contaminants such as salt and calcium carbonate, lubricating properties, filter caking properties, cooling and heat transfer properties, and tolerance to inactive solids such as sand and silt or active native mud making clays such as smectites, illites, kaolinites, chlorites, etc. Those skilled in the art recognize that providing an acceptable drilling mud in the field requires much labor and high material handling and transportation costs. In addition, environmental and occupational safety considerations restrict the types of additives and their amounts in the drilling muds. Also, selected additives should not have fluorescence properties, so that hydrocarbon deposits can be readily identified.
Over the years, a number of drilling mud formulations have been proposed. For example, U.S. Pat. No. 3,726,850 discloses a lignin dispersing agent for dispersing clays, and the like. The lignin dispersing agent is reported to have utility in both alkaline and acidic media. A relatively low viscosity aqueous silicate solution is disclosed in U.S. Pat. No. 3,746,109, and is reported to be particularly useful in drilling through shale formations. U.S. Pat. No. 4,799,549 discloses a stable, gel-forming microemulsion comprising an aqueous solution of an alkali metal silicate, a gelling reagent, and a surface active agent (surfactant). This composition is reported to be useful for permanent or reversible plugging or clogging of subterranean formations. Also, U.S. Pat. No. 5,374,361 discloses a composition for cleaning out cased well-bores, and the like, using a fluid that includes a caustic alkyl polyglycoside surfactant formulation. This formulation is reported to be more biodegradable than previous detergent systems. A further additive encountered in aqueous drilling fluids is a metal compound, such as that described in U.S. Pat. No. 5,399,548, or a derivative of a metal compound such as a hydroxy-aluminum compound admixed with a polymer, such as disclosed in U.S. Pat. No. 4,045,357. U.S. Pat. No. 5,333,698 also discloses a drilling fluid additive in combination with a white non-toxic mineral oil. U.S. Pat. No. 4,780,220 discloses a drilling mud comprising water, a gelling agent and glycerine or polyglycerine.
Various components have been proposed as additives for drilling fluids. U.S. Pat. No. 3,215,634 suggests adding a polymer, a crosslinking agent for the polymer and a polyhydric alcohol to reduce lost circulation in oil field operations. The crosslinking agent can be a compound such as boric acid. U.S. Pat. No. 5,248,665 discloses adding a cyclic ether polyol and optionally a polyol, such as glycerol, to depress the freezing point of drilling fluids. U.S. Pat. No. 5,002,672 discloses using an aqueous composition comprising a glycerophosphoric acid ester and a diacetyltartaric acid ester of a mono or diglycerides in combination with a viscosifier, sealant and a weighting agent as a spotting fluid for releasing a stuck pipe.
Most of the additives discussed above and those employed in the industry are utilized only as additives. That is, they cannot be provided easily, safely, and economically as a "whole mud" system specifically designed to accomplish a given drilling task. Thus, a drilling fluid system is desired which can be applied in a modular fashion with one or more modules being used as needed for a particular set of requirements. Such a system should also enable a person skilled in the art to convert an old mud formulation, e.g., salt muds, lime muds, low solid muds, oil muds, etc., into such a modular system.
There is also an urgent need for improved labor health and safety in working with drilling muds, improved cleanliness of rig flooring and equipment, environmental safety and nontoxicity of additives, as well as reduced handling and storage costs.
To solve the problems of the prior art, the present inventors developed a modular drilling mud or fluid system, filed as application Ser. No. 08/635,354, filed on Apr. 19, 1996, now allowed. This modular drilling fluid system can be conveniently formulated as at least one of the following modules:
(1) an alkaline first module that contains a source of caustic, a natural wax, and a natural thinner; PA1 (2) a second module prepared by reacting aluminum metal with the components of the alkaline first module thereby forming a soluble alkali metal aluminate; PA1 (3) a third module containing the components of the first module in combination with at least one of an alkali metal phosphate and sodium silicate; PA1 (4) a fourth module containing the components of the first module in combination with a C.sub.1-24 saturated or C.sub.2-24 unsaturated carboxylic acid source, a surfactant, and a preservative; and PA1 (5) a fifth module containing the components of the first module in combination with a C.sub.1-24 saturated or C.sub.2-24 unsaturated carboxylic acid source, a surfactant, a preservative, and at least one of an alkali metal phosphate and sodium silicate. PA1 (1) a boost in the lubricity of the modular drilling mud or fluid system, PA1 (2) a boost in the mud thinning or mud viscosity controlling power of the modular drilling mud or fluid system, PA1 (3) a decrease in the strength of the clay particle bond between the drilled clays and the drill bit, or a decrease in bit "balling" tendencies, PA1 (4) a decrease in the rock cohesive or shearing resistance immediately beneath the drill bit, or work front due to penetration of low surface tension dispersants like borates, phosphates and the like into the clay bonds and reduction in capillary entrance pressure due to low surface tension (5 to 35 dynes/cm or the present formulation, and PA1 (5) control of phase separation of the modular drilling mud or fluid system and control of the excessive loss of the mud filtrate to which the modular drilling mud or fluid system is added.
A drilling fluid represented by any of the third, fourth and fifth modules can be used for simultaneous thinning and lubricating operations. A drilling fluid represented by the second module can be used for thickening operations.